The present invention relates to medical devices and more particularly to endovascular devices.
In recent years treatment of aneurysms has included the use of stent grafts that are emplaced within the vascular networks and that include one or more stents affixed to graft material. The stent grafts are secured at a treatment site by endovascular insertion utilizing introducers and catheters, whereafter they are enlarged radially and remain in place by self-attachment to the vessel wall. In particular, stent grafts are known for use in treating descending thoracic and abdominal aortic aneurysms where the stent graft at one end defines a single lumen for placement within the aorta and at the other end is bifurcated to define two lumens, for extending into the branch arteries.
One example of such a stent graft is disclosed in PCT Publication No. WO 98/53761 in which the stent graft includes a sleeve or tube of biocompatible graft material such as Dacron(trademark) polyester fabric (trademark of E. I. DuPont de Nemours and Co.) or polytetrafluoroethylene defining a lumen, and further includes several stents secured therealong, with the stent graft spanning the aneurysm extending along the aorta proximally from the two iliac arteries; the reference also discloses the manner of deploying the stent graft in the patient utilizing an introducer assembly. The graft material-covered portion of the single-lumen proximal end of the stent graft bears against the wall of the aorta above the aneurysm to seal the aneurysm at a location that is spaced distally of the entrances to the renal arteries. Thin wire struts of a proximal stent extension traverse the renal artery entrances without occluding them, since no graft material is utilized along the proximal stent while securing the stent graft in position within the aorta when the stent self-expands. An extension is affixed to one of the legs of the stent graft to extend along a respective iliac artery and, optionally, extensions may be affixed to both legs. Another known stent graft is the Zenith AAA(trademark) stent graft sold by William A. Cook Australia Pty., Brisbane, Australia.
In prior art stent grafts, graft fixation was achieved by fixation at the top or proximal end by barbs or by a stent portion that is uncovered by graft material and could be incorporated into the vessel wall. Distal end fixation was attained by friction within the branch or iliac arteries. The stents of the prior art stent grafts tended to be flexible and relatively soft. The proximal main tube graft was of a standardized length, and that length tended to be significantly shorter than the aneurysms themselves, while the full length was bridged and achieved by smaller diameter extensions or legs.
With the prior art stent grafts, certain late complications were common: due to the above-mentioned configuration there was a certain instability leading to kinking, obstruction of the lumen and/or disintegration leading to possible graft explantation, wherein the stent graft undesirably moved out of its intended position mostly due to larger displacement forces within the smaller diameter stent graft portions; material fatigue also occurred, leading to endoleak wherein blood flow continued into the aneurysm.
The foregoing problems are solved and a technical advance is achieved in the stent graft of the present invention. The stent graft assembly of the present invention includes a main stent graft device or body with an integral ipsilateral leg and a contralateral stump that together define a bifurcation at the distal end, includes a contralateral extension, and further includes an attachment graft tube. The main stent graft body and the attachment tube at its proximal end, will together span the whole aneurysm, but the main stent graft body itself is selected to have a length that is less than the span of the aneurysm, measured proximally from the bifurcation of its ipsilateral limb and the contralateral stump. The proximal end of the main stent graft body is adapted to remain unattached to the vessel wall, unlike conventional stent grafts, but the attachment tube proximal end includes an attachment stent for vessel wall attachment at the aneurysm proximal neck, with the attachment tube fully sealing relative to the aorta while permitting free flow to the renal arteries. Furthermore, in contrast to the prior systems which started positioning at the top, proximally at the renal arteries, the main graft assembly is built starting from below at the distal bifurcation first and extending then from distal to proximal to the renal orifices at the aneurysm""s proximal neck.
After partial deployment wherein the contralateral stump is released from the delivery system sheath, the main stent graft body bifurcation is seated against the aortic vessel wall at the iliac arteries bifurcation, prior to deployment of the ipsilateral leg from the delivery system sheath. The second or attachment graft tube of selected length then is brought up contralaterally through the main stent graft body. The attachment tube is then deployed such that a distal portion of substantial length remains within the proximal end of the main stent graft body to define an overlap region, and an attachment stent extending from the proximal end of the attachment tube is then deployed to attach to the vessel wall at the proximal neck of the aneurysm at the renal arteries. The overlap region may be as little as 2 mm to 5 mm in length but is preferably at least about 20 mm and there is a friction fit between the attachment graft tube distal portion and the main stent graft body proximal portion upon full deployment (expansion) of the stents of the attachment tube. The contralateral limb is thereafter moved into position and affixed to the contralateral stump. Preferably, both the attachment graft tube and the contralateral limb are delivered in a second double-sheath delivery system, through the contralateral artery. Such an overlapping double tube result at the proximal end of the main stent graft body is stronger, and the position of the stent graft assembly after full deployment is more stable against explantation.
Optionally, a third or intragraft tube is placeable into the main stent graft body to underlie and extend in both directions beyond the overlapping region between the main stent graft device and the attachment graft tube. The third graft tube would expand to define a friction fit within both the attachment graft tube and the main stent graft body and have a length greater than the overlap region, thus strengthening the friction fit between the attachment graft tube and the main stent graft body. Such third graft tube would be utilized should configuration changes of the aneurysm, and the subsequent increase in the distance between the renal arteries and the bifurcation, tend to pull the attachment graft tube partially from the main stent graft body and decrease the overlap region therebetween; such intragraft tube can be easily placed during a subsequent procedure.
The present invention is also directed to a first graft member (corresponding to the attachment tube discussed hereinabove) that is to be used in conjunction with at least one other graft member (the main graft tube), and that includes an attachment region having an attachment stent for attachment to a vessel wall, and a distal portion defining another attachment region for attachment to the at least one other graft member.
The present invention includes method aspects: a method of placing an endovascular stent graft in a vessel at a bifurcation thereof where branch vessels join the vessel, for treating an aneurysm thereat, comprising the steps of placing a bifurcated main stent graft body in the aneurysm unattached to a wall of the vessel with a first leg portion in a first branch vessel; urging a bifurcation of the main stent graft body into a seated position against the bifurcation of the vessel to move a second leg portion in a second branch vessel; and securing the stent graft to the vessel wall.
In an additional aspect, the present invention includes a delivery system for endovascular devices, comprising a first sheath having a distal end and a proximal end and containing at least a first expandable device at a proximal end; a second sheath movable within the first sheath and having a respective distal end and a respective proximal end, the respective proximal end concluding distally of the first expandable device and containing a second expandable device; a first pusher associated with the first expandable device extending thereto within the first and second sheathes from a first proximal control pusher end exposed at the distal ends of the first and second sheathes; and a second pusher associated with the second expandable device extending thereto within the first and second sheathes from a second distal control pusher end exposed at the distal ends of the first and second sheathes.